This proposal will continue our ongoing studies of mechanisms of hypertension in coarctation of the aorta using unique experimental canine model in which coarctation is induced in the neonatal period. We have previously demonstrated that, unlike in other hypertensive states, baroreflex sensitivity (BRS) is normal in experimental canine coarctation present from birth, and carotid sinus diameter is increased. We now seek to determine whether this unique preservation of BRS is due to the non-specific presence of hypertension from birth or to the singular mechanical obstruction of coarctation, by assessig BRS both in canine renal hypertension induced at birth and in aortic coarctation induced in adult dogs. Related mechanisms of vasomotor regulation will also be studied in these two preparations and in dogs with neonatal coarctation, to clarify the nature and locus of baroreflex adaptation. These include carotid sinus nerve activity and carotid sinus distensibility. Finally, these studies will also be done after operative correction of coarctation to clarify the currently unknown mechanism by which postoperative "paradoxical" hypertension occurs. Our findings will have implications for understanding and treating hypertension of various types in growing children, for timing operative correction of coarctation, and for preventing and treating post-correction hypertension.